This invention relates to an apparatus for measuring a pulmonary function.
Most of the patients admitted to ICU (Intensive Care Unit) sickrooms are post-operative patients. Recently, an increasing number of people with no experience of operation have been admitted as patients to such sickrooms. Most of these patients suffer from acute respiration failure or insufficiency. Various check methods have at present been studied so as to elevate the quality of checking of respiratory diseases or troubles as well as to effect their earlier diagnosis. A pulmonary function checking effected for the ventilating state of the local area of the lungs is among the important checking lists. A conventional pulmonary function checking method includes, for example, a method for checking a respiratory sound or murmur by a stethoscope and method for measuring the state of a radioisotope (i.e. a gasified radioisotope inhaled through the bronchus) distributed in the alveoli of the lungs by an external scintillator and checking the function of ventilation based on the measured data. The former method is easiest and can locally grasp the dynamic state of ventilation for each respiratory movement, but it is difficult to locate the field of the lungs where the respiratory murmur is produced. The latter method, on the other hand, is complicated, since it requires a radioisotope and computer. Furthermore, it is difficult for the operator to check the pulmonary function in the dynamic state with which each respiration occurs.
Recently, an impedance method has been developed which can check a pulmonary function. This method utilizes a principle on which the respiratory electrical impedance of the thorax vary according to a variation in amount of ventilation. An apparatus for checking a pulmonary function by such an impedance method is disclosed in P. Henderson et al., IEEE Transactions on Biomedical Engineering, Vol. BME-25, No. 3, May 1978. This method measures an impedance distribution over the thorax by a matrix array of electrodes on the thorax and displays the impedance distribution on a display device. In this method, however, impedances measured include an impedance resulting from a contact of each electrode with the skin of the thorax. Since the impedance varies due to the contact state of the electrode, it would be difficult to obtain accurate measurement. Further, the amount of ventilation is merely checked from the overall impedance distribution and it would be difficult to accurately obtain a distribution of air with respect to an accurate amount of respiration of the patient.